This invention relates to recovery of tin from dust produced during tin smelting, and particularly to an efficient method of recovery utilizing a plasma reactor.
The smelting of tin-bearing ores in metallurgical furnaces generates large quantities of dust consisting largely of tin oxides (SnO and SnO.sub.2). This flue dust or smelter dust is typically collected by filtration of hot gases leaving the furnace, then is stored or further processed for recovery of tin. Since the smelter dust may amount to up to about ten percent by weight of the ore feed material, long-term storage or disposal of the large quantities generated presents problems. Known techniques for reprocessing the flue dust, however, also are unsatisfactory. Because direct return of the dust to the smelting furnace would result in a large fraction of the dust being again carried off with furnace gases, current practice is to form the dust into pellets or briquettes and then charge these agglomerates into the furnace. This intermediate processing of the dust typically includes multiple steps such as mixing of the dust with water and chemical binders, then roasting and/or drying the mixture. Also, the resulting pellets often have low mechanical strength and partially crumble during storage or transportation, again yielding flue dust. Overall efficiency of recovery, therefore, may be less than fifty percent.
A more direct technique for processing smelter dusts consisting chiefly of metal oxides of low melting point is the so-called "flash agglomeration" method described in U.S. Pat. No. 4,013,456. In this process, flue dust from lead smelting furnaces is fused at relatively low temperatures, heated with additives, solidified by cooking, then fed to a furnace. This method, however, is not readily applicable to dust containing tin oxides since their melting points are considerably higher than those of lead oxides.
Accordingly, it is an object of the invention to provide an improved method of recovery of tin from dust produced during tin smelting.
It is a particular object of the invention to provide a method of recovering tin from smelter dust without prior agglomeration of the dust.
It is also an object of the invention to provide a method of recovering tin as a liquid from flue dust utilizing a single reactor operating at high yield and low cost.